A network architecture called “IP Multimedia Subsystem” (IMS) has been developed by the 3rd Generation Partnership Project (3GPP) as an open standard for handling multimedia services and sessions in the packet domain.
An IMS Subscriber Identity Module (ISIM) application, or alternatively a Universal Subscriber Identity Module (USIM), stored in a Universal Integrated Circuit Card (UICC) is indispensable to an IMS UE because it contains subscription information that is necessary for the IMS UE to access an IMS network and receive various IMS-based services. The subscription information includes, for example, user identity information such as an IMS Private User Identity (IMPI) and an IMS Public User Identity (IMPU), credentials, and so on.
Taking an IPTV system as an example, any IPTV Terminal Function (ITF), such as a Set Top Box (STB) or TV-set, is required to be authenticated by the IMS network and IPTV system with an ISIM in order to receive IPTV services.
However, not all IMS UEs are necessarily equipped with a UICC. An IMS UE without a UICC must obtain subscription information by some other means in order to access the IMS network. Moreover, it is sometimes desirable even for an IMS UE with a UICC to externally obtain subscription information because the user of the IMS UE may be different from the owner of its UICC. Therefore, a technology for remote ISIM access, that is, a technology that enables the IMS UE to utilize the ISIM of another device, is required.
As of today, several prior art references are known which provide mechanisms, use cases, or service requirements for remote SIM/ISIM access technology as follows:                The 3rd Generation Partnership Project (3GPP) TSG SA WG3 discussed several different models and scenarios where IMS access capabilities are split into two entities, a device like a PC connected to a fixed IP network and a UMTS UE with a UICC. For example, IMS functionality on a PC and ISIM (or USIM) stored in the UICC of the UMTS UE are linked through some interface so that the PC and the UMTS UE can cooperatively act as an IMS UE with the UICC.        A feasibility study was conducted in 3GPP TR 33.817 that presents issues, security threats, potential requirements and the like in an environment where a SIM application is re-used by peripheral devices such as laptop computers or PDAs to be authenticated to mobile operators so that the peripheral devices can access 3GPP and WLAN networks that the mobile operators provide.        The Fixed Mobile Convergence Alliance (FMCA) gives the service requirements for a SIM Access and Authentication service where a SIM in a mobile handset is being used as an authentication token on other user devices for the fixed-mobile convergence environment defined by the FMCA.        A Bluetooth SIM Access Profile provides a means to allow devices such as car phones with built in GSM transceivers to connect to a SIM card in a phone with Bluetooth, so the car phone itself doesn't require a separate SIM card.        